Embodiments of the present invention relate to a compressor unit and a method to process a working fluid.
An industrial plant to extract natural gas from a field present under the seabed is in general placed on a platform above the sea or on the seabed.
In particular, the plant on the seabed comprises a submersible compressor unit and other modules preassembled on the ground and then placed in seabed itself.
The submersible compressor unit comprises generally a centrifugal compressor pushing the extracted natural gas to the mainland and arranged in a housing with an electric motor; this unit could be fluidly connected with an external separator machine placed between the well and the inlet of the unit. This type of compressor unit could be a machine with vertical configuration having a vertical shaft on which is arranged the rotor of the electric motor and also the centrifugal impellers of the compressor, the shaft is supported by a plurality of mechanical bearings and by a thrust bearing, preferably of a magnetic type. The main benefits of the vertical configuration are that the drainage is due to gravity and the footprint is minimized.
These two modules (the compressor unit and the separator machine) are usually provided with respective inlet and outlet openings that are closed with valves during the immersion phase on the seabed; during the installation phase, these two openings are fluidly coupled using a pipe and then the two valves are opened. The best practices include that the valve on the side of the separator machine is opened first; then the valve on the side of the unit is timely opened. In this way the water inside the pipe could be discharged into the separator; the pipe descends from the unit to the separator to facilitate the discharging.
A drawback of this type of machine lies in the fact that the valve of the unit could be opened before the valve of the separator by the operators, provoking the sea water discharge accidentally inside the compressor unit and damaging, the mechanical component of the unit itself.
The patent application WO-2007/103,248 describes a fluid processing machine to process multiphase fluid streams including gas and liquid. A housing has an interior chamber, an inlet fluidly connected with the interior chamber and with a stream source, and first and second outlets. A separator disposed within the housing chamber is fluidly coupled with the inlet such that the stream flows thereto and separates the stream into gaseous and liquid portions. A compressor disposed within the chamber receives and compresses the gaseous portions from the separator for discharge through the housing first outlet, the compressor having an outer surface spaced from the housing inner surface to define a flow passage. A pump provided within the chamber has an inlet fluidly coupled with the separator through the passage, is spaced vertically from the separator so that liquid flows by gravity from the separator to the pump, and pressurizes the liquid for discharge through the housing second outlet.
A disadvantage of this type of machine is that it requires a separator inside the compressor unit, increasing the mechanical complexity and the cost.
Another disadvantage is that the lower mechanical bearing is placed on an inferior baseplate of the housing, and so it is necessary to provide a sealing case to avoid the contact with water or waste. In particular, this case has to be a high sealing case if the bearing is of the magnetic type, increasing the installation and design cost and at the same time decreasing the reliability, that is particularly significant and important for the applications that require a non-stop working for a lot of years, as for example the submerged one.
Moreover, the shaft has to be so long as to place the aforesaid bearing on The baseplate increasing significantly the design cost.
A further disadvantage is that the length of the shaft is related to the vertical length of the chamber, that could vary only if the length of the shaft varies at the same time, increasing the cost and the difficulties for the design.
To date, notwithstanding the developments in technology, this poses a problem and the need exists to produce simpler and cheaper machines to extract natural gas from a field, present under the seabed, improving The installation phase and at the same time the working phase thereof.